System and method for identification and characterization of transglutaminase species

In one aspect, the present disclosure provides a system and method for the identification and characterization of a transglutaminase. Further, the present disclosure provides transglutaminase enzymes for forming isopeptide bonds, methods of forming isopeptide bonds in the presence of transglutaminases, and substrate tags for use with transglutaminases. In another aspect, the present disclosure provides glutamine-containing substrates (or Q-tag substrates) that are more resistant to proteases/clipping and therefore, more stable, than other Q-tag substrates, and their uses in substrate tags for cross-linking to an amine-donor tag via an isopeptide bond mediated by a microbial transglutaminase.